1. Field
The present embodiments relate to a nonvolatile semiconductor memory device.
2. Description of the Related Art
As an electrically rewritable and highly integratable nonvolatile semiconductor memory device, a NAND flash memory is known. The memory cells of the NAND flash memory each include a semiconductor substrate, a charge accumulation layer formed on the substrate via a tunnel insulating film, and a control gate stacked on the charge accumulation layer via an inter-gate dielectric film. Each memory cell stores data in a nonvolatile manner using the charge accumulation state of the charge accumulation layer.
The NAND flash memory performs, after an erase operation of the memory cells, an erase verify operation of verifying whether the memory cells are erased to a desired state. If the erase verify operation cannot be performed correctly, the memory cells will be applied repeatedly with the erase voltage, which may degrade the memory cells.